Implementing a load balancer with child processes in Node.js

10 Oct 2023

In a Node.js application, a load balancer is a critical component that helps distribute incoming requests across multiple worker processes or servers. This helps in achieving high availability and scalability for your application. In this blog post, we will explore how to implement a simple load balancer using child processes in Node.js.

Introduction
Step 1: Creating the Master Process
Step 2: Spawning Child Processes
Step 3: Routing Incoming Requests
Step 4: Handling Failures
Conclusion

Introduction

A load balancer acts as a reverse proxy that sits between the client and the application servers. It receives incoming requests and evenly distributes them among the available worker processes.

In our implementation, we will use the built-in child_process module in Node.js to spawn multiple child processes that will handle the incoming requests.

Step 1: Creating the Master Process

The master process is responsible for creating and managing the child processes. It also listens for incoming requests and routes them to the child processes.

const http = require('http');
const { fork } = require('child_process');

const server = http.createServer();

server.on('request', (req, res) => {
  const childProcess = fork('./worker.js');
  
  childProcess.send({ req });
  childProcess.on('message', (response) => {
    res.end(response);
    childProcess.kill();
  });
});

server.listen(3000, () => {
  console.log('Load balancer listening on port 3000');
});

Step 2: Spawning Child Processes

In this step, we’ll create a separate file called worker.js, which will be the entry point for each child process. This file will handle the actual processing of requests.

const http = require('http');

const server = http.createServer((req, res) => {
  // Process the request here
  res.end('Hello from worker');
});

process.on('message', ({ req }) => {
  server.emit('request', req, res);
});

Step 3: Routing Incoming Requests

When a request is received in the master process, we create a new child process using fork and send the request to it using the send method. The child process listens for incoming messages and emits the request event on the server object, which triggers the same event in the child process.

Step 4: Handling Failures

In a production environment, it’s important to handle failures gracefully. If a child process crashes or becomes unresponsive, the master process can detect it and take appropriate action. For example, it can restart the child process, remove it from the active pool, or notify an external monitoring system.

Conclusion

In this blog post, we learned how to implement a simple load balancer using child processes in Node.js. This approach allows us to distribute incoming requests among multiple worker processes, achieving high availability and scalability for our applications. However, keep in mind that this is a basic implementation, and in a real-world scenario, you would need to handle various edge cases and add additional features to make it production-ready.

#nodejs #loadbalancer

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